defecation. Of course the chief of these con-
ditions consists in the application of a stimulus
to the large intestine itself. And though any
irritation of the mucous membrane of the
rectum seems capable of producing that vio-
lent straining which marks the exertion of
the abdominal pressure, still its strictly co-
ordinate character is well illustrated by the
preference apparently shown to a stimulus
which acts directly on the muscular fibres of
the bowel themselves. Thus a mechanical
distention of the rectum appears to be a more
efficient stimulus to the total expulsive act
than the application of any ordinary irritant.
While, vice versa, there are good reasons for
conjecturing, that mere distention of the
belly is capable of arousing a sluggish large
intestine to expel its contents.f And a
* See p. 316.
t Such a " reflex action," from the animal to the
organic muscle, may perhaps explain the operation
of one of the ordinary remedies against constipation ;
STOMACH AND INTESTINE.
371
still more frequent association of movement
is probably exemplified in the tenesmus pro-
duced by dysentery and other disorders, which
involve great irritation of the rectum. For
the sensations of the patient, and the uncon-
trollable impulse which follows them, seem
to indicate that the irritation of the mucous
membrane is often accompanied by violent
contraction of the muscular coat of the in-
testine, both of which unite to excite the
subsequent abdominal pressure.
The nature of the contents of the rectum
greatly affects the degree in which the muscles
of the abdomen are made to assist in their
expulsion. When these contents consist only
of gases and liquids, they require so little of
this aid, as to be sometimes expelled without
it. But the extrusion of hard scybalous
evacuations often demands the help of ab-
dominal pressure, to an extent such as in-
volves all the viscera of the trunk, and
seriously obstructs the flow of blood in the
larger veins of the head and thorax.
As regards the levator ani muscle, its origin
and insertion, together with the course taken
by its fibres, leave no doubt as to what must
be the direct effect of its contraction. It
raises the end of the rectum, together with
the ligamentous structures of the perinaeum
anteriorly, and the coccyx posteriorly. But
as the time of this action seems exactly to
coincide with the exertion of the abdominal
pressure just alluded to, the degree in which
it really raises these structures can only equal
the surplus of its force over that of the mus-
cles of the belly. Hence it may be doubted
whether the muscle generally does more than
fix the bowel : an effect which is, however,
of the highest importance to the mechanism
of defalcation. The influence of the neigh-
bouring perinaeal muscles is still more obscure.
Such being the known agents of the pro-
cess of defalcation, we may next attempt to
sketch the course of its phenomena.
The ordinary peristalsis of the large in-
testine propels into the rectum a variable
quantity of faeces. These, after a longer or
shorter sojourn in its first or second por-
tions, excite an active peristaltic contraction
of its muscular coat. In general it is only
when they reach the lower extremity of the
bowel, that the abdominal pressure adds to
this peristalsis its far more powerful expulsive
force. The combined effect of both these
actions urges the faecal mass against the ex-
ternal sphincter, which relaxes at this in-
stant, by a voluntary effort, so as to permit
the extrusion of the descending mass : a small
portion of the loose mucous membrane being
at the same time generally everted around it.
A variable length of faecal substance thus
passes through the orifice of the anus. The
continuity of the descending mass being finally
interrupted, the act of respiration* is resumed ;
the abdominal pressure ceases; and at the
same time, the contraction of the levator ani,
aided by that of the rectum itself, returns the
projecting extremity of the bowel into the
pelvis, by a kind of sudden and forcible re-
traction. The latter act, in which both of
the sphincters may be presumed to play an
important part, often subdivides a continuous
faecal mass ; returning the upper segment
thus cut off into the cavity of the rectum
which it was just leaving. The total du-
ration of the expulsive act appears to be
chiefly determined by the consistence of the
fasces, the velocity of their transit, and the
exigencies of the suspended process of respi-
ration itself.
The mucous membrane of the rectum is con-
nected with its muscular coat much more
loosely than that of the colon. Owing to
this circumstance, it generally exhibits nume-
rous folds. Most of these are mere tempo-
rary results of the passive contraction of the
muscular coat. And in correspondence with
such an origin, they are very irregular in
size, number, and position. They are, how-
ever, more frequently found occupying the
dilated lower end of the bowel, where they
take what is usually a longitudinal direction. __ *
But in addition to such casual and tem-
porary folds, Mr. Houston* has described
others, which he states to have a definite
direction and situation, as well as a more
permanent character. According to this
anatomist, three is the number of these folds
or valves usually present. The largest and
most constant of the three projects from the
anterior wall of the rectum, opposite to the
base of the bladder, and about three inches
above the anus. The valve next above this
springs from the left wall of the bowel, about
midway between the last and the third or up-
permost fold. This latter projects from the
right wall of the upper end of the rectum.
The shape of all three is nearly semilunar :
their depth about half an inch ; and they are
fixed by a convex border to about half the
circumference of the intestine. And Kohl-
rausch-|- has described a fold which tolerably
answers to the fourth and least constant of
those mentioned by Mr. Houston. He states it
to be always present, as a transverse projection
from the posterior wall of the rectum opposite
the middle of the coccyx. In general it con-
tains no muscular fibres : but rarely these may
even encircle the bowel, as a continuous ring
or third sphincter, which forms the lower
boundary of a dilated and sacciform segment
of the rectum.
As regards these folds, we may point out,
that their usual situation corresponds to
the most prominent parts of those three
curves of the rectum which we have already
alluded to. Thus the third answers to that
convex mucous surface which marks the
namely, the application of a wet bandage tightly * Dublin Hospital Reports, \
around the belly. t ^ur Anatomic und Fhvsi
The way in which this act is affected during
the exercise of abdominal pressure has already been
explained at p. 316.
s, vol. v. p. 163.
" Zur Anatomie und Physiologic derBeckenor-
gane," Leipzig, 1854 ; also Valentin's " Bericht
ueber die Leistungen in der Physiologic " in Can-
statt's Jahresbericht, 1854.
BBS
372
STOMACH AND INTESTINE.
transition of the sigmoid flexure of the
colon into the rectum ; the second indicates
the spot where the bowel reaches the median
line of the sacrum ; and the first is nearly op-
posite to its bend in the hollow of the latter
bone and the coccyx. And frequent as their
presence undoubtedly is and important as
they therefore are with respect to the surgery
of the rectum, it may still be doubted
whether they possess those characteristic
anatomical features that would alone entitle
them to rank as true permanent folds, like the
transverse or falciform septa which isolate the
several pouches of the large intestine. For,
unlike these, they are not only somewhat irre-
gular in number and position, but are effaced
by complete distention of the tube. And,
finally, they appear to contain not a trace of
the proper transverse stratum of unstriped
fibres. Hence they probably exp/ess a mere
passive arrangement of the loose mucous
membrane; a relaxation which is perhaps
chiefly due to contraction of the powerful
longitudinal layer of the muscular coat of the
bowel.
In the rectum, the muscular lamina of the
mucous membrane resumes its usual thick-
ness. At the lower part of the bowel, the
skin and mucous membrane become con-
tinuous with each other. But, as might be
expected from the great dissimilarity of these
structures, there is a distinct line of demarcation
between the two. Their junction is situate,
not exactly at the anus, but at a point from
two to four or five lines above this aperture.
Here the skin terminates by a wavy margin,
having a distant resemblance with that dentate
edge, by which the thick white epithelium of
the oesophagus adjoins the delicate pink mu-
cous membrane of the stomach. And the
apex of each of these waves usually corre-
sponds to the starting point of a longitudinal
fold of mucous membrane ; which, after pro-
ceeding a short distance up the bowel, either
becomes indistinct and disappears, or is crossed
and effaced by others that take a different
direction. It is nearly in this situation that
Kohlrausch * describes a thin layer of un-
striped muscular fibres, lying between the
sphincter ani internus and the mucous mem-
brane. Traced upwards from their intimate
union with the latter structure, these fibres
are seen to take a longitudinal course; and
to end, about one and a half inches above
the aperture of the anus, by joining the layer
of circular fibres immediately external to them.
Regarding these latter as their origin, it is
evident that their action would raise the mu-
cous membrane, and oppose its prolapse.
Hence they are described as forming a " sus-
tentator tuniccB mucosce" Below its junction
with the mucous membrane, the moist skin
possesses its ordinary structure. And around
the anus, it is occupied by numerous hair
bulbs ; as well as by sebaceous follicles, which
pour forth a large quantity of a peculiar odo-
rous secretion.
The contents of the large intestine are of
* Loc. cit.
two kinds. The first is a mass which, usually
of a semifluid consistence, ranges from the
state of a thin liquid to that of a hard friable
solid. This mass, when evacuated from the
rectum, constitutes the faeces, ordure, or ex-
crement. The second is an elastic or ga-
seous fluid, which occupies the intestine in
very variable amount, and unless its quantity
be excessive, is not necessarily or regularly
expelled at all.
Fceces. It will be some clue to the compo-
sition of the faeces if we recollect, that the
large intestine so far resembles the small, as
to justify our inferring that it continues the
various metamorphoses which the contents
of the canal begin to undergo in its upper
segments. These metamorphoses are due,
partly to a spontaneous decomposition of
the alimentary substances themselves, partly
to changes set up by the various secretions
mixed with them. And they are accom-
panied by processes of absorption and se-
cretion, which may probably be regarded
as in some degree peculiar to this segment
of the tube. Of these two processes, that
of absorption seems chiefly destined to de-
prive the intestinal contents of their more
watery and soluble parts. While the act of
secretion pours forth fluids which, from their
proximity to the end of the bowel, may be
assumed to be, in great extent, excremen-
titious. The matters thus excreted may be
divided, histologically, into two chief con-
stituents : a structureless alkaline fluid
which is furnished by the tubes ; and a scaly
epithelium, which is a desquamation from the
mucous membrane of the rectum.
But it would be wrong to suppose that
the whole of the processes which engage
the contents of the large intestine can be
comprehended in three such acts of meta-
morphosis, absorption, and secretion as those
just alluded to. On the contrary, each of
these three exerts its usual complex reaction
upon the other two. Thus the soluble re-
sults of metamorphosis undergo absorption,
as do also some of the substances secreted.
The fluids secreted into the bowel no doubt
modify the spontaneous changes which en-
gage its contents. And, finally, the slow
transit of these contents along the intestine
is accompanied by the precipitation of in-
soluble matters from the various secretions
of the upper segments of the canal, prior to
their expulsion from its lower orifice.
It has indeed been alleged, that the ccecum
is the seat of a special metamorphosis, which
repeats, as it were, the process of gastric
digestion: that its mucous membrane pours
out an acid secretion, which is capable of dis-
solving certain constituents of the food pre-
paratory to their absorption. But a closer
examination dispels this view, and assigns to
this segment an humbler office, which is
closely analogous to that of the neighbouring
portions of the canal. Its tubes, which have
precisely the structure of those found else-
where, pour out an equally alkaline secretion.
Its infusion, whether acidulated or otherwise,
STOMACH AND INTESTINE.
has no higher solvent power over albuminous
substances than that possessed by the similar
fluid prepared from pieces of ileum or colon.
While the strongly acid reaction of its contents
in many herbivorous animals is sufficiently
explained as due to that lactic fermentation,
which the various starchy substances are so
apt to undergo when exposed to spontaneous
decomposition at the temperature (about*
103) of the intestinal canal. Consistently with
such an explanation, this acid reaction is found
chiefly or exclusively in those parts of the
faecal mass which are not in contact with
the alkaline mucous membrane, and is by
no means limited to the contents of the coecal
pouch.
We may therefore regard the faeces as com-
posed chiefly of two constituents : which
are derived, the one from the food taken by
the animal, and the other, from the secretions
of its digestive organs. And in like manner,
we may" premise what follows by stating,
that the composition of any particular excre-
ment will always depend on the nature of the
food, the state of the secretions, and the na-
ture and amount of the metamorphoses which
both these constituents have together under-
gone.
Physical properties of the faces Subject to
circumstances so numerous and fluctuating, it
is obvious that the physical properties of the
faeces must vary extremely in different sub-
jects. Their ordinary colour, odour, form,
size, and consistence are so well known, as
scarcely to require any special description in
this essay.
As regards the two first of these characters,
the contents of the small intestine are dis-
tinctly faecal. But it is only in the coecum,
where both their colour and odour become
much more marked, that the faeces usually
begin to acquire a solid consistence. Their
form and size is dictated, partly by the
shape and diameter of the bowel (as already
alluded -f- to), and partly by the degree in which
their consistence has been augmented by the
absorption of their watery parts. Where
their solidity is much increased from this
latter cause," the act of expulsion has little
influence in modifying their form. The way
in which it usually does this has been
previously pointed out.
The odour and colour peculiar to the faeces
have been ascribed, by some authors, to the
bile which enters into their composition ; by
others, to the fluids which are poured out
into the intestinal canal from the blood-vessels
occupying its mucous membrane. It is, how-
ever, probable that they are not due to either
of these causes exclusively, but depend rather
on a combination of both; and are further mo-
dified by that admixture of altered (not to say
decomposing) food, which forms so large a
constituent of the excrement.
Thus, that they depend to some extent on
the bile, is well shown by those cases of
* Brown Sequard, " Experimental Researches in
Physiology and Pathology," New York, 1853.
t See p. 366.
jaundice, in which a deficient secretion of this
fluid, or an obstruction of its normal channel,
has arrested its flow into the intestine. For
in such instances, the ordinary brownish yel-
low tint, and faecal smell, proper to the excre-
ment, are exchanged for a greyish white co-
lour, and an intensely putrefactive odour.
But it is certain that, unless the bile be
poured out in excessive amount (as after the
exhibition of mercury *), or conveyed through
the bowels with unusual rapidity (as in diarrhoea
and purging), it is but a small fraction of its
total quantity that escapes re-absorption, so as
to be found in the fasces. This statement
especially applies to the meconium which
occupies the intestine of the foetus. At any
rate, this substance contains but little of the
acid or the colouring matter of ordinary bile.
Now, the preparation of excrement by the
foetus, and by hybernating or starving animals,
is a satisfactory proof that its specific faecal
characters are not essentially due to any modifi-
cation of the alimentary matters contained in
the intestinal canal. And since the bile forms
but a small portion of its mass, it is evident
that much of it must be derived from the se-
cretions of the digestive tube itself, and that its
properties must be partially due to the same
source. Indeed, this intestinal constituent,
which is probably always a large ingredient
of the faeces, becomes, in the hybernant and
the foetus by far the largest : so much so,
that the dried meconium contains about 85
to 95 per cent, of epithelium and mucus, al-
most all of which must be referred to this
source. While, as regards its physiological
import, it is impossible to doubt that it is
(/car* i^oxr) v) the excrement : that it is, in fact,
the chief excretory ingredient of the faeces ;
and hence that ingredient, the dismissal of
which from the intestinal canal is most essen-
tial to the welfare of the organism generally.
The above view, as to the share which both
the biliary and the intestinal constituents take
in producing the colour and odour of the
faeces, appears so irrefragable, that we may
content ourselves with a passing allusion to
those experiments by which it has been at-
tempted to establish the predominant or exclu-
sive influence of either. Thus, while it has
been pointed out by Valentin -f- that putre-
fying bile diffuses the strongest smell of or-
dure, LiebigJ states that he has succeeded in
the artificial production of the faecal odour by
a process which essentially consists in imper-
fectly oxidizing some of the more azotized tis-
sues of the body. The latter experiment has
been regarded as leading to the inference, that
* The green colour of the stools after calomel has
been taken seems to be due, partly to the chemical
reaction of the contents of the intestine, partly to
an increase in the quantity of bile poured out. The
latter fact has been confirmed by experiments, in
which this drug has been administered to dogs pro-
vided with biliary fistulas opening externally. The
chemical change "undergone by the mercury in the
intestinal tube consists (like that of the "salts of
iron under similar circumstances) in the formation
of a sulphuret of the metal.
f Lehrbuch der Physiologic, vol. i., p. 370.
J Animal Chemistry, 3rd ed., p. 148. et seq.
BBS
374
STOMACH AND INTESTINE.
certain effete constituents of the blood are
secreted into the intestine, in a like state of
partial oxidation. But, even could we assume
the chemical identity of two substances merely
from their having the same overpowering smell,
we should still be left in uncertainty, as to
whether these odorous matters were excreted
directly from the blood into the bowel, or were
introduced into it indirectly, by means of the
secretion and subsequent metamorphosis of
the bile. The very large intestinal constituent
of the meconium, associated as it is with an
almost inodorous character of this excrement,
would indicate that, on the whole, Valentin's
view of the biliary origin of the faecal odour is
the more correct one. At present, however,
a satisfactory decision of the question seems
impossible.
But whether the peculiar odour of the faeces
be biliary or intestinal, there can be no doubt
that it is derived, in the first instance, from
the blood. For the smell of the excrement
of any particular species always has a close
relation to that odour, which is specific to the
body of the animal, and which appears, in va-
rious degrees of intensity, in all its different
excretions. And it is even stated by Wehsarg*
to present differences specific to the individual.
Finally, we need have little scruple in as-
serting, that all the physical properties of the
faeces are also in a great measure dependent on
that alimentary residuum which usually enters
so largely into their composition. The quan-
tity of fatty matter and of casein usually pre-
sent in the excrement of the sucking-child,
the deepening (and finally black) colour of the
faeces in persons who feed chiefly on vege-
tables, the lactic acid found in the evacuations
of carnivora, or the oil which may often be de-
tected in the stools of persons by whom even
small doses of cod-liver oil are being taken
medicinally form instances of this kind,
which might obviously be multiplied to almost
any extent. Nor is the process always li-
mited to a mere admixture or decomposition
of the food itself. On the contrary, the
metamorphoses which most of its ingredients
have to undergo, often react on the secretory
contents of the canal, so as to modify their
appearances by the addition of properties
more or less foreign to them. And nothing
but that comparatively uniform admixture of
the chief alimentary principles of the food,
which we shall hereafter find is absolutely
necessary to the life of the individual, will
account for even the imperfect uniformity
traceable in examining the excrements of
large numbers of individuals.
The reaction of the human faeces is gene-
rally acid; sometimes neutral or alkaline. The
quantity daily evacuated by a healthy male
adult may be estimated as amounting, on an
average to about five ounces avoirdupois.
The specific gravity of the faeces is gene-
rally greater than that of water, owing to the
solids which they contain. But it is far too
variable to allow of any average estimate
* Microscopische und ChemischeUntersuchungen
der Fasces gesunder Menschen. Giessen, 1853.
being made. For it varies, not merely with
the bulk and weight of the alimentary resi-
due that forms so large a portion of the or-
dinary excrement, but also with the degree
in which the faecal mass has been condensed
by the absorption of its watery constituents.
And it would further seem, that the faeces are
capable of being partially dried, and rendered
much lighter, by a mechanical admixture of
intestinal gases with th/eir substance while
still within the body. At least it is very
common for different portions of the same
evacuation to exhibit very different specific
gravities: the first portions of the excre-
ment, which previously occupied the lower
extremity of the rectum, being much lighter
than water; while those subsequently extruded,
though less solid, are so much heavier, as to
sink rapidly in this liquid.
The mechanical composition of the excre-
ment might almost be deduced from what
has already been said of its origin. A large
quantity of its mass no doubt consists of un-
digested food.* This must, however, be sub-
divided into two parts, which have a very
different import with respect to the digestive
function. One of these, which is usually
much the larger, includes all those substances
that are incapable of being dissolved by the
various secretions poured into the intestinal
canal. Such are the harder parts of various
animal and vegetable tissues : the sarco-
lemma of muscular substance, the cells of car-
tilage, fragments of bone, the elastic fibres of
areolar tissue ; together with the husks, shells,
pods, chlorophyll, epidermis, and various
dense membranes, cells, vessels, and fibres
of the various fruits and seeds used as food.
Some of these tissues quite defend the soluble
contents they enclose. The other portion
consists of substances which, though really
capable of solution in the alimentary canal,
have escaped this process: whether from
having been taken in too large a quantity,
from not having sojourned in the tube during
a sufficient interval of time, or from having
been exposed to secretions which are par-